Where is friction needed in a backhoe loader?

You would need friction between the tires or tracks and the dirt the tractor is sitting.

If you have extended legs, you need friction between the pads and the ground.

You would want friction in the brakes.

A clutch also relies on friction.

Technically you could "dig water", but if you are trenching, then one needs friction between the dirt particles.

It is also handy to have friction in your seat, steps, and controls.